Kourosh Saberi, Ph.D. - US grants

The long-term objective of the proposed research is to improve our understanding of how the binaural system facilitates the detection and recognition of complex sounds (i.e, sounds that have a bandwidth) in the presence of masking sounds. To date, few studies have provided an in depth investigation of binaural unmasking of complex signals and none has modeled the relevant results. The proposal has three specific goals: 1) to improve our understanding of how complex binaural objects are formed and localized, particularly when multiple images are detected, 2) to determine the degree to which the unmasking of a complex signal is dependent on the perceived spatial separation of the signal and masker, and 3) to develop, improve, and evaluate binaural- based models of unmasking capable of predicting the benefits to complex-signal detection. Two experimental paradigms are used. First, a complex signal (narrowband noise, or a multi-tone complex) is alternated with an acoustic pointer which the observer adjusts to match the perceived spatial position of the signal. In the second experimental paradigm, the degree to which spatial position affects unmasking is examined. Here, a complex sound (either a narrowband of noise, an AM or FM carrier, a two-tone complex, or a sequence of tone bursts defined by the pattern of intertone times) is presented in a background of a complex masker. The subject is required to indicate in which of two observation intervals the signal was presented. Both energetic and informational masking will be examined. The magnitude of binaural unmasking is usually very large, as great as 30 dB for narrowband maskers, and therefore has strong influences on auditory perception in natural environments. The results of the current experiments are expected to have further benefits for multi-channel hearing-aid design, and for basic theory and models of binaural interaction.

Natural sounds are complex high-dimensional signals. The "cocktail-party phenomenon" in the hearing sciences is a classic example of the brain's ability to parse out and attend to a particular dynamic signal (speech) in the presence of multiple extraneous (non-signal) sounds, all of which reach the ears concurrently and continuously vary in pitch and location as a function of time. The ability to identify a relevant signal out of this "acoustic mixture" far outdistances that of the most sophisticated current automated speech-recognition systems. To understand how people process complex sounds that dynamically vary in time, space, and frequency, scientists must determine how the brain organizes these auditory dimensions. With support from the National Science Foundation, Dr. Saberi and his colleagues will use neuroimaging techniques to systematically map the neural landscape that underlies the functional organization of brain regions responsive to temporal, spatial, and spectral aspects of complex sounds.

The broader impacts of this project include applications to automated speech-recognition systems, development of auditory navigation systems for the blind, improved signal-processing by auditory prostheses for the hard-of-hearing and cochlear-implant users, and a deeper understanding of cortically-based auditory deficits in humans. The project integrates research and education by providing opportunities for graduate and undergraduate students to engage in research, and by complementing the planned development of an undergraduate and Ph.D. program in cognitive neuroscience at UCI and an interdisciplinary Center for Cognitive Neuroscience.

DESCRIPTION (provided by applicant): The functional anatomy of the planum temporale (PT) has been of great theoretical interest for decades, and a focus of recent clinical studies of a number of disorders ranging from autism to schizophrenia. Although the (left) PT was initially thought to subserve language functions, recent basic research has shown that it is multifunctional, being implicated in such diverse processing domains as speech perception and production, tonal processing, auditory-motor integration, spatial hearing, and multi-sensory integration. Given the potential importance of the PT in both theoretical models of cortical function for a range of abilities as well as its widespread clinical implications, a more thorough understanding of the functional organization of the PT is sorely needed. The present proposal seeks to fill this gap through a series of fMRI studies using within subject designs, and organized around four specific aims. Aim 1 is to assess activation patterns for several functions known to activate the PT, including speech perception/production, tonal/melodic perception, sensory-motor integration, visual speech perception, and spatial hearing. Aim 2 seeks to understand the functional basis for sensory-motor activations in the PT. Sensory-motor behaviors have been strongly associated with the PT (particular on the left) both clinically and functionally. This aim examines whether PT sensory-motor activations are more strongly aligned with the auditory system (as is typically thought) or to the vocal tract articulator system (as we have recently hypothesized). In addition, we examine this system's role in temporal sequence processing, which we believe is connected to sensory-motor function. Aim 3 is to identify neural networks supporting the interaction of spatial hearing and speech processing. Both speech-related and spatial hearing- related functions have been associated with PT function. We examine a possible interaction of these two functions in connection with auditory stream segmentation, in particular whether activation in the PT reflects the use of spatial cues to segment auditory information into distinct objects. Finally, Aim 4 is to map the relation between spatial-speech integration and visual-speech integration. It is well known that auditory stream segregation processes can make use not only of spatial cues, but also of visual speech cues. Interestingly, processing both of these cues involves the PT suggesting a possible connection. PUBLIC HEALTH RELEVANCE The proposed research is of importance from a public-health standpoint because in recent clinical studies the planum temporale has been implicated in a number of disorders ranging from autism to schizophrenia. This brain region appears to be involved in several critical functions from language processing to integration of auditory, visual, and motor functions. In spite of its central role in sensory/cognitive functions, very little is known about how this brain area is organized, and given its widespread clinical importance, a more thorough understanding of the functional organization of this region may lead to more effective treatment strategies for cognitive dysfunctions.

Our brains have evolved a highly-sophisticated auditory system for the analysis of sounds, which underlies more complicated abilities such as speech perception. We currently know very little about the organization of human auditory cortex at the interface between the auditory inputs from the peripheral sensory receptors in the ear and the higher-level language systems of the brain. Understanding the nature of the inputs to higher-level speech perception systems is critical to understanding what kind of information is ultimately used in speech perception and how this information is extracted computationally. With support from the National Science Foundation, Dr. Alyssa Brewer and colleagues Dr. Gregory Hickok and Dr. Kourosh Saberi will use functional magnetic resonance imaging (fMRI) to measure the functional organization of the human auditory cortex with a level of detail that has not previously been achieved. They will then use these measurements to examine how cortical responses to particular types of speech and speech-related stimuli relate to these lower-level cortical regions. This study will thus provide the first systematic measurements of the human speech perception system from the fundamental organization of auditory cortex to cortical speech representations.

Acquired and developmental disorders of hearing, speech and language affect millions of individuals. The knowledge gained from this study will give us a better understanding of the organization and function of these systems, which will have clinical benefits for the treatment of both peripheral auditory diseases and central language disorders. The research team will continue to share the results through "Brain Day" programs in the local K-8 elementary schools to bring the excitement of neuroscience research to the local communities. Furthermore, PI Brewer has developed ongoing "Brilliant Brain" workshops with Girls Inc., which include special presentations and summer workshops on the organization, function, and diseases of the brain. Girls Inc. is a non-profit organization that provides research and STEM-based experiences to girls ages 6-18 across the U.S. and Canada designed to help them navigate gender, economic, and social barriers. Finally, this study incorporates training of new neuroscientists at the undergraduate, graduate, and postdoctoral levels for whom these studies will serve as a foundation of neuroscience research.